The support of the hanging wall in stopes is one of the most basic requirements in underground mining operations. Dependant on the type and quality of rock being supported, the depth of mining, the prevalent field stresses, seismicity, stoping width and a number of other factors, underground mine roof support can vary across a vast range of materials, configurations and systems. These include, amongst others, timber poles, timber and composite packs, steel props, unmined ore pillars, rock anchors and granular or tailings type supports.
Among granular support media, cemented grout packs are increasingly being used as combination support products. These consist essentially of a support column formed by cured cemented backfill or other suitable cured cementitious grout which is contained within a geotextile bag and generally stiffened with external restraining rings or metal mesh against lateral deformation or bulging during installation and when yielding under subsequent axial load.
Conventional grout bags are essentially closed geotextile containers, typically made of woven ribbons and monofilaments of polyethylene and polypropylene to provide required filtering characteristics to retain solid particles whilst allowing excess liquid to escape. Of course, it is also possible that the grout bag could be water impervious any event that the unset cementitious grout is sufficiently devoid of any excess moisture. The bag has some form of unidirectional valve for inflating it with slurry under pressure. The bags also typically have some means of suspending them on support structures within the stopes using ties or loops to facilitate their installation. Once the bags have been inflated with slurry, typically as a grout, the material needs to cure or set to develop sufficient strength to carry load.
However, not all grades of tailings are suitable for use as grout for inflating such a grout bag and, in particular, the fines or slimes as they may be termed would, if they could be used practically, require uneconomical amounts of cementitious material to be admixed therewith. Accordingly, the use of grout bags to form grout packs, whilst it does assist in the disposal of some of the tailings generated consequent on the mining operations, it does not assist as regards the disposal of tailings having a fine particle size.